signal only knows a phone number in association with an account creation date and the last sent message date. everything else is encrypted.
Thats not really possible. If thats all they give out, then that just means that is all that they decide to save. They have access to the servers that everyones messages pass through. They could log the IP and date for every single message sent if they wanted to, but just decide not to do it. This model fails however as soon as they are forced to save more than that.